Push the current matrix stack down by one, duplicating the current matrix, excute the given action, and pop the current matrix stack, replacing the current matrix with the one below it on the stack (i.e. restoring it to its previous state). The returned value is that of the given action. Note that a round-trip to the server is probably required. For a more efficient version, see unsafePreservingMatrix.

O(min(n,W)). Delete the maximal key. Returns an empty map if the map is empty.
Note that this is a change of behaviour for consistency with Map versions prior to 0.5 threw an error if the IntMap was already empty.

O(min(n,W)). Delete the minimal key. Returns an empty map if the map is empty.
Note that this is a change of behaviour for consistency with Map versions prior to 0.5 threw an error if the IntMap was already empty.